Miniature bipolar cylindrical magnets are used as the drive element (rotor) in electromagnetic components such as electromagnetic camera shutter actuators. To ensure proper and reliable shutter performance, the polarization (operating point) and orientation of the magnets need to be controlled to a high degree of accuracy. However, during the mass production of these magnets significant variations occur in both of these characteristics. These variations are due to non-uniformity's of the bulk materials from which the magnets are cut and from variations in the magnetizing field strength over the group of magnets that are bulk magnetized. Moreover, experience indicates that it is difficult, if not impossible, to eliminate both of these causes.
There have been several attempts to provide an apparatus and method for rapidly determining de magnetization and orientation for purposes of selecting only those magnets that have acceptable values.
Referring to FIG. 1, one such existing apparatus 1, disclosed in Research Disclosure No. 37841, dated October 1995, comprises a rectangular ferromagnetic core 11 with two gap regions 2 and 3. A field sensor 4 is positioned in gap region 3 that is connected to a Gaussmeter 5, and a first angular meter device 6. First angular meter device 6 further comprises a first needle pointer 7 connected to a first support member 8 that is mounted for rotation about a pivot axis 9, and a marked scale 10 for determining the angular deflection of the first needle pointer 7 from the vertical straight up position (illustrated in FIG. 1). The ferromagnetic core 11 and the first angular meter device 6 are mounted on a frame 12 that is constructed from a non-magnetic material such as aluminum. The core 11 is fixed to the frame 12 whereas the first angular meter device 6 is mounted for translation along the frame 12 as indicated by the solid arrow in FIG. 1.
Referring to FIG. 2, a second prior art apparatus 14 (also disclosed in the above referenced Research Disclosure) for rapidly determining the orientation of miniature bipolar magnets for purposes of selection for assembly is illustrated. According to FIG. 2, the apparatus 14 comprises a second angular meter device 16 that is mounted for linear translation relative to a stationary member 18. The second angular meter device 16, made from non-magnetic material, comprises a second needle pointer 20 connected to a second support member 22 that is mounted for rotation about a pivot axis 24. As shown in FIG. 2, second angular metering device 16 further includes a marked scale 26 for determining the angular deflection of the second needle pointer 20 from its detent position. The second support member 22 which is mounted for rotation has a top portion (not shown) that is designed to hold a miniature bipolar magnet that is to be tested. The stationary member 18 is made from non-magnetic steel and comprises a base 28, and support structure 30 which supports two ferromagnetic pole pieces 32a and 32b that are in a spaced-apart relation. The second angular meter device 16 is mounted for translation as indicated by the dotted arrow in FIG. 2.
Referring again to FIG. 1, an existing method for evaluating the polarization and orientation of miniature bipolar magnets 40 include the step of initially providing first angular meter device 6 in position A, separated from core 11. A miniature bipolar cylindrical magnet 40 is mounted on first support member 8 of first angular meter device 6 with its "anticipated" north pole 40a vertically up. In this initial position, first needle pointer 7 is straight up indicating 0 degrees of deflection on the marked scale 10. The first angular meter device 6 is then moved to position B as illustrated until the magnet 40 is symmetrically positioned in gap region 2 of core 11. The magnet 40 will then align itself in the gap 2 so that its "true" north pole 40a is symmetrically positioned with respect to tapered pole tip 2a. If the "true" north pole 40a is offset in an angular sense from the "anticipated" north pole, the magnet 40 will rotate and first needle pointer 7 will deflect indicating the angular offset on the marked scale 10. In this way, the orientation of the magnet 40 is determined. Once the magnet 40 has oriented itself, it comes to rest. In its rest position, the flux from the magnet 40 passes through the core 11 and is directed through gap region 3 where the field sensor 4 is located. The field through the sensor 4 is registered on Gaussmeter 5. This registered field value is compared to a calibration field value from a known magnet. In this way, the magnetization of the magnet 40 is determined. Depending on the results of the test, the magnet 40 is either accepted or rejected.
A shortcoming of the aforementioned existing apparatus and method for screening bipolar magnets 40 is that they do not have the ability to verify manufacturing variability and magnetization in complex magnetic rotors. More importantly, existing apparatus and methods, as described above, do not have the ability to compare magnetic flux density of a magnet with angular position or angular position of certain post features with reference to magnetic poles. Moreover, existing models do not have the ability to display acquired data and then compare such data with predetermined calibrated complex magnetic elements, such as magnetic rotors.
Therefore, a need persists in the art for a measurement apparatus and method that can generate specific magnetic flux and angular position data of bipolar miniature magnets for determining their acceptability for use in electromagnetic components, such as high speed shutter applications.